Extraskeletal osteosarcoma in Norway, between 1975 and 2009, and a brief review of the literature.

AIM To evaluate the clinicopathological features of extraskeletal osteosarcoma (ESOS) and its response to multimodal therapy. PATIENTS AND METHODS A nationwide cohort comprising all Norwegian histologically verified ESOS patients between 1975 and 2009 supplemented with clinical reports from all hospitals involved in sarcoma management. RESULTS Thirty-seven patients were classified as ESOS, mostly elderly people. Seventy-six % had an axial tumour, including nine patients with radiation-induced ESOS. The gender balance was equal. The 5-year sarcoma-specific survival (SSS) was 16 %. Adequate surgical remission had a positive impact on SSS, in contrast to chemotherapy and radiotherapy. Primary metastatic disease, elevated tumour size and elevated serum alkaline phosphatase, serum lactate dehydrogenase and Ki67, respectively, all predicted poor outcome. CONCLUSION The relatively poor prognosis of ESOS may relate to both primary chemotherapy resistance and different biologic characteristics of these tumours as compared to conventional osteosarcoma. Hence, new predictive molecular markers and therapeutic approaches for treatment of ESOS are needed.